With development of technology, chip integrated level is constantly improved, the number of I/O pins increases dramatically, power consumption also increases accordingly, and requirements on integrated circuit packaging are more stringent. In order to meet the needs of development, Ball Grid Array (briefly referred to as BGA) packaging begins to be used in production. The BGA is an advanced packaging technology which interconnects an integrated circuit (IC) and a substrate. The IC is adhered onto a plastic or a ceramic substrate. In a case of the BGA packaging, spherical solder balls attached to the IC package will be placed on an electrical connection pad of a printed circuit board (a circuit substrate) with a layer of flux. Then the circuit board will be heated to a certain temperature to melt the flux and all the solder balls, to fuse with a conductive pad formed on the printed circuit board below. Hence, the IC can be connected to the printed circuit board without an external lead.
In a printed circuit board layout (PCB Layout) stage, forms and specifications of the BGA packaging as well as a number of the pads decide that via holes must be disposed in the circuit board so that wires can be led out of positions of the pads, and be connected to other parts and electrical pads.
FIG. 1 is a structural schematic diagram of a conventional printed circuit board with a ball grid array structure. As illustrated in FIG. 1, a printed circuit board 100 has pads 110, via holes 120 and conductive circuits 130 disposed thereon. As can be seen from FIG. 1, all the via holes 120 are disposed in gaps between a plurality of pads 110. In this case, molding drawings are very messy, engineers of printed circuit board layout need to spend a lot of time to distinguish the pads required to be wired first. In addition, for such ball grid array used by the printed circuit board with a layout of such a high density, during wiring, even the outlets of the two peripheral rows of pads 110 must be connected to inner conductive layers through the via holes, but cannot be led out from a TOP layer. Thus, the via holes on the TOP layer have no practical meaning. Furthermore, in the conventional printed circuit board for the ball grid array structure, the pads and the inner layer circuits must be connected through the via holes by means of connecting lines, for example, as illustrated in FIG. 1, the adjacent pads and via holes are connected by connecting lines represented by thick lines and thin lines.